-98.6% is the change from 645 to 9
Calculation steps:
[( 9 - 645 ) ÷ 645] x 100 = -98.6%
Formula
Percentage change = [(9 - 645) / 645] x 100
Subtract the new number by the original number
9 - 645 = -636
-636 ÷ 645 = -0.986046511627907
-0.986046511627907 x 100 = -98.6%